The present invention relates to dry processes for treating the surfaces of solids, and more particularly to a surface treatment method and apparatus which can realize a damage-free, contamination-free, highly selective and low temperature process well suited to the fabrication of semiconductor devices. In the fields of surface treatments, especially the field of the fabrication of semiconductor devices, dry processes have been often adopted for about ten years. Here, the "dry process+ is an expression as opposed to a wet process (a method employing an aqueous solution) practised before, and it is a method in which the surface of a sample is treated in vacuum (including light) or in a gaseous phase. In the conventional dry process, a plasma or an ion beam has been used as the gaseous phase, and the kinetic energies of electrons, ions and the ion beam entering the sample surface have been distributed at several eV-10.sup.4 eV (refer to FIG. 2). Meanwhile, the displacement energy of an atom within a crystal (energy required for displacing an atom from the regular crystal lattice position thereof), E.sub.d is about 10 eV. By way of example, E.sub.d =12.9 eV holds in an Si crystal (G. Carter and J. S. Colligon, "Ion Bombardment of Solids", Heineman Educational Books Ltd., London, 1968, p. 214). With the dry process, therefore, damages have heretofore been inevitably formed in the sample surface. Moreover, the temperature of the sample has risen due to the entrance of such high energy particles and has sometimes exceeded 300.degree. C. Such a temperature rise of the sample has formed other crystal defects (damages) in the sample surface or has extremely narrowed the application range of the process. Besides, when such high energy particles have entered the surface of a solid near the sample, they have physically and chemically sputtered the surface substance, and the sputtered substance has re-deposited on the sample surface to contaminate it. As the dimensions of semiconductor devices decrease (to 1 .mu.m or less), the damages, contamination and device temperature rise as stated above become serious problems. In addition, such damages, contamination and temperature rise will be fatal to three-dimensional semiconductor devices expected to be realized in the near future, and the conventional dry processes will become unfeasible.
Essential items which ought to be done in surface treatments are to remove the substances of the sample surface through physical and chemical reactions on the sample surface or in the gaseous phase (etching), to deposit a substance on the sample surface (deposition or epitaxy), and to modify the characteristics of the substance of the sample surface (any of oxidation, nitridation, etc.). In this case, the chemical reactions play the principal roles rather than the physical reactions. The reason is that the chemical reactions can realize more reactive varieties. Now, energy levels concerning the chemical reactions (chemical bond energy) are distributed at 0.01-10 eV as shown in FIG. 2, and energy which gives rise to crystal defects is about 10 eV. Accordingly, a range of 0.01-10 eV is suitable as energy levels which are employed for executing the surface treatment. In actuality, however, all the energy supplied to the surface is not consumed for forming the crystal defects. Therefore, the upper limit of the energy can be increased about 10 times. That is, approximately 0.01-100 eV are the optimum as the energy which is supplied to the surface in order to perform the surface treatment.
As indicated in FIG. 2, the magnitudes of energies possessed by atoms or molecules (hereinbelow, termed "species"), namely, the rotational energy of molecules, the vibrational energy of molecules, the electronic energy of atoms or molecules and the translational energy of atoms or molecules can be controlled into the energy range (0.01-100 eV) mentioned above. Accordingly, these energies can be employed as the supply energy to the surface for performing the surface treatment. That is, atoms or molecules the whole energy E.sub.w of which falls within the range of 0.01-100 eV (hereinbelow, such atoms or molecules shall be termed "active species") are caused to enter the surface thereby to perform the surface treatment, whereby the surface treatment having no surface damage (or having very little surface damages) can be carried out. Here, the whole energy E.sub.w is expressed as: EQU E.sub.w =E.sub.r +E.sub.v +E.sub.e +E.sub.t
E.sub.r : rotational energy, PA0 E.sub.v : vibrational energy, PA0 E.sub.e : electronic energy, PA0 E.sub.t : translational energy.
A surface treatment method wherein a molecular beam in which a vibrational state E.sub.v among the states of the four kinds of energies (E.sub.r, E.sub.v, E.sub.e, E.sub.t) is excited is projected on a sample so as to treat the surface thereof, is disclosed in the official gazette of Japanese Patent Application Laid-open No. 113775/1986. In addition, a surface treatment apparatus wherein a gas is heated to excite the rotational state, vibrational state and electronic state of gas species, which are thereafter emitted into vacuum and turned into a beam, which is projected on a sample so as to treat it, is disclosed in the official gazette of Japanse Patent Application Laid-open No. 35521/1988 (U. S. Patent Application Ser. No. 891,641, now U.S. Pat. No. 4,697,836). As indicated in FIG. 2, however, the maximum value of the vibrational energy is at most 1 eV, and even the energy of the electronic state does not reach 100 eV. Insofar as the aforementioned value of 100 eV is not exceeded, the energy of the species with which the sample is irradiated should desirably be greater because the throughput of the surface treatment can be raised. Nevertheless, an energy level higher than 10 odd eV cannot be attained by the energies of the rotational state, vibrational state and electronic state which are utilized for the energy supply to the sample in the prior-art techniques. Besides, it is difficult that these energies are independently controlled so as to adjust the species beam to a desired energy level. Further, these energies are discrete and cannot be set at any desired energy levels.